Question

Which of the following is a Gattermann reaction?

• A. \(\mathrm{ArN_2^+X^- \xrightarrow{CuCl/HCl} ArCl + N_2 \uparrow}\)
• B. \(\mathrm{ArN_2^+X^- \xrightarrow{HBF_4} ArN_2^+BF_4^- \rightarrow ArF + N_2 \uparrow + BF_3}\)
• C. \(\mathrm{ArN_2^+X^- \xrightarrow{Cu/HBr} ArBr + N_2 \uparrow}\)
• D. \(\mathrm{ArN_2^+X^- \xrightarrow{KI,\ \Delta} ArI + N_2 \uparrow + KX}\)

Hint:

Gattermann reaction uses \textbf{Cu + HX} (not cuprous salts) to replace diazonium groups by Cl or Br.

Answer 1

The Correct Option is C

Step 1: Recall Gattermann reaction.
In the Gattermann reaction, aromatic diazonium salts are converted into aryl chlorides or bromides using copper powder and corresponding hydrogen halide (HCl/HBr).

Step 2: Differentiate from similar reactions.
Sandmeyer reaction uses cuprous salts (CuCl/CuBr).
Balz–Schiemann reaction gives aryl fluorides using \(\mathrm{HBF_4}\).
Iodination with KI directly replaces the diazonium group without copper.

Step 3: Identify the correct option.
Option (C) uses \(\mathrm{Cu/HBr}\), which matches the Gattermann reaction conditions.

Step 4: Conclusion.
Thus, option (C) represents the Gattermann reaction.